Personality disorders (PD) are serious, debilitating, costly, and oftentimes fatal disorders that are highly prevalent in epidemiological samples (~10 percent, Lenzenweger, 2008). Despite the severity and high public health cost of PD, the field suffers from a lack of consensus on how to best quantify the relationship between normative personality and PD. This lack of consensus has led to problems in basic definitional issues of PD, including the structure, course, and risk/protective factors of the disorders. The criteria of most PD diagnoses include maladaptive interpersonal behaviors (e.g., Interpersonal Exploitativeness in Narcissistic PD). The interpersonal traits of Agency and Communion have been identified as potentially useful for developing a dimensional model of PD. Further, interpersonal conceptualizations of personality are highly useful for linking with PD due to their immediate implications for psychotherapeutic interventions. Additionally, emerging research has shown that PDs are not as chronic as once thought, showing considerable variability across time. The current research aims to meet the strategic planning goals of the National Institute of Mental Health by using state-of-the-art methodology to articulate emerging conceptions of PD that account for simultaneous change in interpersonal behavior and PD over time, and non-normality in the distribution of PD. Specifically, we propose using Latent Growth Curve Models and associated multivariate extensions to examine change and distribution of PD in a multi-wave prospective longitudinal study. This research shall test the hypotheses that 1) there is long-term within-person variability in interpersonal style across time;2) within-person variations in interpersonal style are predictive of concurrent within-person variations in PD symptoms;and 3) advanced distributional assumptions (i.e., Zero Inflated Poisson/Negative Binomial) provide a better fit for models of the relationship between PD and normative personality structure. These methods have the potential to inform classification questions in ways that have not yet been employed in any longitudinal PD research to date. Results of the proposed study have implications for the ongoing efforts to establish the appropriate definition, diagnosis, and treatment of PD. The results will inform the best approach to conceptualize classification and assessment of PD. In addition, the longitudinal nature of these studies will identify the interpersonal maintenance factors of PD, and thereby determine the best targets for interventions. PUBLIC HEALTH RELEVANCE: Results of the proposed study have implications for the ongoing efforts to establish the appropriate definition, diagnosis, and treatment of personality disorders (PD). The results will inform the best approach to conceptualize classification and assessment of PD. In addition, the longitudinal nature of these studies will identify the interpersonal maintenance factors of PD, and thereby determine the best targets for interventions.